[rollei_list] Re: Question about Rollei Filters and compensation

I heard somewhere that Plus-X can reproduce an infrared like effect by using an 87c filter. Although I've yet to try it, it does point to variance with emulsion sensitivities. Then there are the various orthochromatic emulsions, & Ilford's SFX, not to mention the slew of Maco emulsions.


Slobodan Dimitrov
Studio G-8,
Angels Gate Cultural Center
http://sdimitrovphoto.com





On Nov 28, 2005, at 6:55 PM, Richard Knoppow wrote:


----- Original Message ----- From: "Eric Goldstein" <egoldste@xxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Monday, November 28, 2005 5:55 PM
Subject: [rollei_list] Re: Question about Rollei Filters and compensation


Richard Knoppow wrote: (snipped)

I think this is the case but it suggests that the filter factor is no more than a sort of average guide and may be wrong for some types of objects of scenes.


This is the very point that Slo D. made. Different films are more and less sentitive to different portions of the spectrum, and there is a huge creative call that needs to be made...


Eric Goldstein
---

I am not so sure there is that much difference in spectral sensitivity among films of similar types. By similar I mean, for instance, general purpose pan films as contrasted with tablular grain films or films with special sensitization such as Technical Pan or traffic recording film.
Presumably, the fact that most film has a much larger tollerance for overexposure than for underexposure also tends to affect required filter factors, i.e., a little too much is better than too little. Maybe. Again, the nature of the colors in the scene and their desired rendition in monochrome is important, but how does one define the "correct" exposure.
Obviously, if a red filter is used the color of everything in the scene becomes a shade of red and the _average_ light level is reduced. But, consider the unlikely case of an all-red scene. The transmission of the filter will be nearly 100% there (or lets define it so for sake of argument). This suggests that the exposure will be the same, or nearly so, regardles of the presence or absence of the filter. Is this logic wrong?

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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